A comprehensive analysis of alpha- and flavivirus proteins will be undertaken to obtain detailed knowledge of the structure and function of these proteins and their relationship to their virus life cycles. Viruses from both groups are significant human pathogens and several have been identified as possible biological weapons. We will employ a high-throughput approach to examine each of the viral proteins from representative members of the two virus groups. This will be accomplished using X-ray crystallography (Chen, Rossmann, Smith) to examine the atomic structure of the viral proteins or complexes of proteins. Cryo-electron microscopy (cryo-EM) will be employed to examine the structure of the individual viruses and their intermediates in assembly and entry (Baker, Rossmann). Knowledge obtained from structural studies will be applied to molecular genetic and biochemical approaches using viruses or replicons (Kuhn, Strauss). In vitro assays will be developed to examine various aspects of the replication cycle such as RNA replication, protein processing, particle assembly, and virus fusion (Baker, Chen, Kuhn, Rossmann, Smith, Strauss). The long-term goal of this proposal is to understand the life cycles of these two virus groups at the atomic level and to translate this information into novel antiviral (Chen, Kuhn, Rossmann, Smith) and vaccine (Baker, Kuhn, Rossmann, Strauss) approaches to control human infections. The proximity of the individual laboratories on the same floor of one building permits exchange of crystallographic (Chen, Rossmann, Smith) and cryo-EM (Baker, Rossmann) expertise as well as virological and molecular biological techniques (Kuhn). Collaborations on alphaviruses and flaviviruses have been ongoing between a subset of the PIs for more than a decade (Baker, Kuhn, Rossmann) and have expanded to include a newly hired faculty member (Chen) as well as a senior crystallographic investigator (Smith). Collaborations between the Strauss laboratory and the Purdue Structural Virology Group have grown in recent years and this is reflected in the conviction that the Strauss laboratory, although removed from the Purdue environment, will contribute significantly to the long-term successes of the project.